The present invention relates to an improved information recording method and apparatus in which magnetic latent images are formed on a recording medium by a magnetic head, and the magnetic latent images are developed to visible images by a magnetic toner; and more particularly to an information recording method and apparatus of the above type in which the magnetic toner and the magnetic-latent-image-bearing recording medium are electrically charged to the same polarity, so that the magnetic toner is electrostatically repelled from the recording medium in the background areas of the images, even where magnetic latent image-like patterns that should not be developed have been formed, while, in the image areas, the attraction between the magnetic toner and the magnetic latent images predominates over the electrostatic repulsion between the magnetic toner and the recording medium, whereby the magnetic toner is deposited on those magnetic latent images in the intended image area only.
In the conventional information recording method and apparatus of this type, the background areas on a magnetic recording medium, outside the magnetic latent image areas, are occasionally slightly magnetized when a magnetic latent image is formed, for instance, due to the formation of a closed magnetic field by the magnetic recording head during the latent image formation process. If magnetic latent images on a recording medium with such a magnetized background are subjected to development by use of a magnetic toner, both the magnetic latent images and the background are developed, though to differing degrees. This is the so-called "deposition of toner on the background" or "fog of the background." It occurs because one end portion of each magnetic toner particle is polarized to an N pole, while the other is polarized to an S pole, and, when the background is magnetized (to whatever polarity), the toner particles are attracted thereto and deposited thereon.